1. Field of the Invention
The present invention relates to a multiplexer, a transmission apparatus, and a reception apparatus that include elastic wave filters.
2. Description of the Related Art
Recent cellular phones are required to support a plurality of frequency bands and a plurality of wireless communication schemes, so-called, multi-bands and multi-modes with a single terminal. To meet such requirements, a multiplexer that demultiplexes a high-frequency signal having a plurality of radio carrier frequencies is disposed right under a single antenna. Elastic wave filters that characteristically have low loss in a pass band and sharp band pass characteristics around the pass band are used as a plurality of band pass filters included in such a multiplexer.
International Publication No. 2016/208670 discloses a surface acoustic wave (SAW) device (SAW duplexer) including a plurality of SAW filters that are connected to one another. Specifically, an inductance element is connected in series between an antenna element and a connection path of an antenna terminal and reception and transmission SAW filters to achieve impedance matching between the antenna element and the antenna terminal. With this inductance element, complex impedance obtained by viewing capacitive SAW filters from the antenna terminal to which the capacitive SAW filters are connected is successfully adjusted to approach the characteristic impedance. In this way, degradation of insertion loss is successfully prevented.
However, in the case of impedance matching of the related art that is achieved by connecting an inductance element in series to an antenna terminal, the Q factor of the series-connected inductance element greatly influences insertion loss. For example, when an inductance element having a low Q factor such as an inductance element disposed in a package is used, insertion loss degrades in the pass band of each filter. In particular, insertion loss of a filter (Band 25 reception filter, for example) for which an inductance element is connected in series between the filter and the antenna terminal defining and functioning as a common terminal degrades in the pass band more than insertion loss of a filter not including such an inductance element.